Fire alarm systems have used a variety of technologies to attempt to provide audible or visible warnings of the existence of a fire condition to individuals in an area being monitored. In one known type of system, ambient condition detectors such as smoke, flame or thermal detectors are distributed in an area to be monitored. These units are often coupled via a communication link to a common control console or control panel.
The panel, in some instances, is capable of analyzing signals received from detectors to ascertain the presence of a fire condition. In other systems, a fire determination is made at the respective detectors and a signal indicative thereof is fed back to the control panel.
The above-described alarm systems are often used in combination with sprinkler systems. Known sprinkler systems incorporate sprinkler heads which are coupled to sources of fire suppressing liquids, such as water, or non-aqueous chemical suppressants.
The sprinkler heads are usually sealed with metals having relatively low temperature melting points. In response to the presence of heat from a fire, these metals soften and melt and release a fire suppressant.
Waterflow detectors have been used in such distribution systems to provide an indication that one or more of the sprinkler heads is delivering water to a portion of the region being monitored. Such waterflow detectors are disclosed, for example, in U.S. Pat. Nos. 4,782,333 entitled Waterflow Detector having Rapid Switching and 4,791,414 entitled Waterflow Detector. Both of the noted patents are assigned to the assignee hereof and are incorporated by reference herein.
Outputs from the waterflow detectors can in turn be used to directly energize alarm indicating visual or audible loads. Alternately, such signals can be coupled to an alarm system control panel for the purpose of providing additional warnings.
It is known that, from time to time, transient movement of water in a distribution system can occur in response to non-fire conditions. Such transient movement can be caused, by example, by intra-system water surges due to various causes.
Known water flow sensors often incorporate mechanical timers to incorporate a delay in an attempt to suppress such transience thereby minimizing false alarming. Known timers suffer from variability of the delays that are provided due to the mechanical timing mechanisms.
It would be desirable to provide highly repeatable transient suppressing delay intervals for use with waterflow sensors. Preferably such repeatable delay intervals could be achieved without introducing additional manufacturing complexity or manufacturing costs. It would also be desirable to be able to minimize power dissipation during no flow conditions.